Modulated-signal generator



Aug. 10, 1948.

R. C. HERGENROTHER MODULATED SIGNAL GENERATOR 3 Sheets-Sheet 1 Filed Feb. 21, 1946 mm N m 5 I 4 6 4 O I 2 H 2 n 0 w 2 I I I O I O 2 I I m 4 I I W 2 III I I I 3 II I, I. I

I 5 IIIII I1 /I\\ 5 II I. 2 I I 6 I Ii I 5 3 8 2 7 m. 3 3 7 0 2 5 d 5 ,J I Q H. I 6 I 9 a 3 3 5 F 5 M Time-I- IN V EN TOR.

I R E H m R N 4 E G R E H C RU DOLF BY 7/ ATTORNEY.

3 Sheets-Sheet 2 v INVENTOR. RUDOL C. HERGENROTHER,

' A TORNEY.

R. c. HERGENROTHER MODULATED SIGNAL GENERATOR a l O m 4 B P. PM u w. m m d I\ o M Aug. 10, 1948.

Filed Feb. 21, 1946 Patented Aug. 10, 1948 UNITED STATES PATENT OFFICE MODULATED-SIGNAL GENERATOR Rudolf C. Hergenrother, West Newton, Mesa, as-

signor, by mesne assignments,

to Hazeltine Research, Inc., Chicago, Ill., a corporation of' Illinois Application February 21, 1946, Serial No. 649,344 Claims. (Cl. 179-1715) This invention relates, in general. to moduinitiate and sustain oscillations therein in order 1 to generate a modulated-carrier signal having a similar wave form. In operation, the modulating potential causes the circuit conductance to decrease to zero and then increase to a high negative value. The negative conductance causes 0s cillations to build up in an exponential manner from an initial value corresponding to the level of the inherent background disturbance of the oscillatory circuit which, for convenience, may be called the circuit noise signal. Usually, the modulating potential is sufficiently long in duration that the oscillations attain a maximum or saturation value. At the trailing edge of the modulating potential, the oscillations decay and the circuit is restored to its normal nonoscillatory-condition.

It has been found that a finite time is required for the oscillations to build up to their maximum value. The build-up time is usually variable, be ing influenced bysuch factors as the level of the erratic noise signal at the start of the negativeconductance interval, the type oscillatory circuit employed, and the condition of the oscillator tubes. It represents an uncertain time delay between the leading edges of the modulating pulse and the generated signal and its effect may be considered as a shortening of the generated signal which, ideally, is intended to start and stop coincidentally with the modulating potential.

The build-up time or delay phenomenon referred to may become very objectionable in particular installations. Since it is generally a noncontrollable and variable efiect, it introduces an undesired instability manifested by the generation of pulse signals of unequal pulse widths in response to modulating potentials of uniform duration. The instability is most pronounced in arrangements designed to produce output signals having a build-up time comparable with Q cycles of the oscillation, where Q is the ratiooi reactance to resistance effective in the loaded oscillatory circuit. In such cases the delay in starting may constitute an appreciable part of the desired pulse period. Additionally, the build-up time impairs theefliciency of the oscillation generator because during such time energy is supplied but no useful output signal is produced.

It is an object of the present invention, therefore, to provide an improved modulated-signal generator which avoids, at least in part, the aforementioned limitations of prior arrangements.

It is a further object of the invention to provide a modulated-signal generator having improved stability and efiiciency characteristics.

It is a specific object of the invention to provide an improved modulated-signal generator controlled by a modulating potential of step wave form to produce an output signal of similar wave form having a leading portion occurring in sub stantial time coincidence with the corresponding portion of the modulating potential.

A modulated-signal generator in accordance with the invention comprises an oscillatory circuit including a cavity resonator normally maintained in a nonoscillatory condition and having an inherent background disturbance the amplitude of which is normally much less than a predetermined value. The generator has means, for applying to the oscillatory circuit a pulse of modulating potential having a leading sloped portion to initiate therein oscillations of the aforesaid predetermined value. Additionally, it includes a transient-signal generator positioned at least in part within the cavity resonator and having an operating interval not exceeding the duration of the leading sloped portion of the modulating potential. Circuit connections are provided for exciting the transient-signal generator to introduce a signal into the cavity resonator to increase the amplitude of the background disturbance to a level much greater than its normal'value. The background disturbance has this increased amplitude for an interval which occurs in approximate time coincidence with but of a duration not exceeding the leading sloped portion of the modulating potential, whereby the oscillations initiated in the oscillatory circuit build up to the aforesaid predetermined value rapidly to provide a modulated-carrier signal envelope with a leading sloped portion occurring in approximate time coincidence with the leading sloped portion of the modulating potential.

For a better understanding of the present invention, together with other and further objects thereof, reference is had to'the following description taken in connection with the accompanying drawings, and its scope will be pointed out in the appended claims.

In the drawings, Fig. 1 represents a modulatedsignal generator embodying the present invention in one form; Fig. 2 comprises curves utilized in explaining the operation of the Fig. 1 arrangement; Fig. 3 represents a signal generator including the invention in a modified form; Fig. 4 is a schematic representation of still another generator arrangement in accordance with the invention: and Fig. 5 includes graphs utilized in explaining the operation of the arrangement of Fig. 4.

Referring now more particularly to Fig. 1 of the drawings, there is represented a cross-sectional view of a modulated-signal generator constructed for ultra-short-wave operation and including the present invention in one form. This generator essentially comprises an oscillatory circuit normally maintained in a nonoscillatory condition and having an inherent background disturbance the amplitude of which is normally much less than a predetermined value. As illustrated, the oscillatory circuit is provided by anelectron-discharge device ill, or vacuum tube of the triode type, and a pair 01' associated resonant cavities II and I2. Tube I is the so-called lighthouse" tube having an anode ii, an anode ring I4, a control electrode ring I and a conductive shell is capacitively coupled to a cathode electrode (not shown). The tube also has conventional terminal prongs to facilitate making connections to a suitable source of heater voltage but, for the sake of simplicity, the prongs have been omitted from the drawing.

The first resonant cavityi I includes a cylindrical hollow inner conductor and a cylindrical hollow outer conductor 2| which are maintained in fixed concentric relationship by insulating spacers 22 secured between the conductors at points suitably spaced around the periphery thereof. One end of inner conductor 20 is open but its other end is closed by a disc 23. Disc 23 is centrally apertured to accommodat an electrical connector for yieldably engaging the anode II of tube Hi. The connector is provided by a stack of resilient laminations 25 which may be secured to disc 23 by way of machine screws 20. The corresponding end of outer conductor ii is likewise closed by a centrally apertured diaphragm 21. Within its aperture there is mounted an electrical connector 28 for yieldably engaging the control-electrode ring I5 of tube I 0. The opposite end of outer conductor 2| is closed by a disc 29 which adjustably supports a, cylindrical tuning plunger 30 in coaxial alignment with inner conductor 20. The plunger 30 has an appreciably smaller diameter than that of the inner conductor and forms a re-entrant portion of outer conductor 2| through which the operating wave length of the oscillatory circuit may be adjusted.

The second resonant cavity I2 is generally similar to that just described, including an inner hollow cylindrical conductor and a concentrically disposed outer hollow conductor 36 which may constitute an extension of conductor. A conductive ring 31 maintains the desired space relationship of conductors 35 and 38. Another conductive ring (not shown) may be positioned above ring 31, having a slidable engagement with conductors 35 and 36 to tune resonant cavity l2. The end of conductor 35 adjacent diaphragm 21 is closed by a disc 38 arranged to accommodate a connector 39 constructed like connector 25 but proportioned yieldably to engage the cathode shell I6 of tube Ill. An adjustable probe 40 projects through an aperture of diaphragm 21 and aflords a feed-back path between resonant cavities I I and I2, as required to sustain oscillations upon the application of suitable operating potentials to the oscillatory circuit.

The generator, as thus far described, is similar to that disclosed and claimed in a copending 4 application of Harold A. Wheeler, entitled Ultrashort-wave signal-translating device," Serial No. 565,828, tiled November 30, 1944 and assigned to the same assignee as the present invention. Ref erence may be had to this copending application for a more detailed discussion of the mechanical and electrical properties oi a generator 01' the type under consideration. As there described, however, the generator is energized to produce conl0 tinuous oscillations whereas in the instant application pulse-modulated operation is contemplated. To this end, means are provided for applying to the oscillatory circuit a modulating potential of step wave form to initiate therein oscillations of 15 a predetermined value, corresponding to saturation level. More specifically, a terminal for receiving a modulating pulse of positive polarity is coupled by. way of a bushing-type condenser 4i and a signal-frequency choke 41 to inner con- 20 ductor 20 of resonant cavity II.

In order that the generated oscillations may reach saturation level early in the period of the applied modulated pulse, means are included in the generator for eflectively increasing the ampli- 25 tude of its background disturbance or noisesignal to'a level much greater than its normal level for a short time interval, occurring in approximate time coincidence with but of a duration not exceeding the leading sloped portion of the applied 80 pulse of modulating potential. This means includes an arc-discharge or spark-gap device positioned within resonant cavity I I and having a pair of electrodes 6i and 52 adjacent ends 01' which are sealed within a hydrogen-filled 35 envelope. Electrod BI is conductively connected with inner conductor 20 and may serve to support the spark-gap device within cavity resonator I I. Its other electrode 52 is capacitively coupled with -a projecting or chimney-like portion 53 of outer 4Q conductor II, this coupling being designated by a. condenser 54 shown in broken-line construction since it comprises distributed rather than lumped capacitance. This simulated capacitance 54 is serially connected with spark-gap device 50 45, through inner conductor 20 to the modulatingpulse terminal 45.

The signal generated in the oscillatory circuit is derived through a pickup loop 51 and supplied to any suitable utilizing circuit through a coaxial- 50 type cable 58. The cable and pickup loop may be positioned within resonant cavity I I through a second chimney-like portion 59 of outer conductor 2!. This conductor is grounded as indicated at 60.

In considering the operation of the Fig. 1 arrangement, the generator will be seen to comprise a triode vacuum tube In having a first resonant cavity II coupled to its anode and control electrodes and a second resonant cavity I2 coupled 0 to its cathode and control electrodes with a feedback therebetween provided by probe 40. The first of these cavities determines the operating wave length of the generator. The second is proportioned so that the arrangement represents an oscillatory circuit similar to the well-known Colpitts oscillator, the operation of which is well understood in the art. The performance of the oscillator under the control of modulating potentials'oi' step wave form is demonstrated by the curves of Fig. 2.

The applied modulating potential is represented by the full-line curve A. It is a pulse of excitation potential having stepped or sloped portions at both its leading and trailing edges. The

application 01' this pulse to inner conductor 20 saturation value.

establishes a potential gradient across the Bap electrodes II and II. when this potential gradient exceeds the breakdown potential or the spark gap, device is rendered conductive. Current then flows through the spark gap; as represented by curve-B, being interrupted upon the charging I Asin any'gas-niled trodes reaches breakdown value.

time should be less than that of one-quarter of a some time is required for the gap-current to build up after the potential gradient across. its elec- Preferably, this cycle at the operating wave length of the generaoccurs within the duration of the leading sloped portion of, the modulating potential, as indicated V by curves A and 2B. I

' The flow of current through troduces a signal into-resonant cavity II which causes the inherent background disturbance or noise level oi. the oscillator to be much greater the spark gap inthan that encountered when the oscillator is blocked and the spark gap is nonconducting. Since this increased signal level occurs early in the duration of the leading sloped portion of the modulating potential, the resulting oscillations have a high initial value and build up to their maximum level rapidly, as indicated by dash-dot curve C. The spark current is, preferably, interrupted within the duration of the leading sloped portion of the modulating potential so that this maximum value corresponds with the saturation level. The oscillations are maintained throughout the duration of the modulating pulse and generate a modulated-carrier signal. At the end of the modulating pulse, condenser 54 discharges through device 50 and the generator is restored to its normal nonoscillatory condition. Curve C represents one-half of the envelope of the output signal derived by pickup loop 51. It-has a leading sloped portion occurring in approximate time coincidence with the corresponding sloped portion of the modulating potential and, therefore, an approximately equal pulse duration.

The dotted curve D illustrates the circuit operation in the absence of the spark gap. In such a case, the generated oscillations have an initial value corresponding to that of the circuit background disturbance at the time the modulating pulse is applied. This initial level is much smaller than that occasioned by the breakdown of the spark-gap'device and accordingly a greater time interval is required for the oscillations to attain The improvement in build-up time attributable to spark-gap device 50 is indicated Atl in Fig. 2. The decrease in build-up time increases the efliciency of the oscillator and causes the envelope of the generated pulse to conform more closely with the Wave form of the modulating potential. Additionally, the spark-gap device improves the stability of the oscillator sothat the generated signals obtained during succeeding modulating intervals are substantially uniform if the modulating pulse in each case has approximately the same wave form.

In one embodiment of the Fig. 1 arrangement, found to have practical utility, tube 10 was an R. M. A. No. 2042 operated under the following conditions:

tor to ensure that the gap contains signal energy of this wave length. For many applications-a gap of about 1 mil in an atmosphere of hydrogen is suitable.

v The generator arrangement of Fig. 3 embodies the invention in modified form. This generator also includesa triode-type vacuum tube having a rod-type cathode 80, a. ring-type anode CI and a control electrode or grid 82. The grid is in the form oi. a cage interposed between the cathode and a longitudinal extensionof the anode and is supported by a grid post 88. At one end of the grid there is a radiator 64, comprising a stack of spaced metallic discs. A plurality of straps 85 are secured across the discs of the radiator and provide a conductive path through a contact element 86 to the grid post 83. Glass portions 81 and 88, having metal-to-glass seals with grid member 66, the anode extension, and the cathode 60, complete the tube envelope.

As in the Fig. 1 arrangement, a pair of cavity resonators l0 and II are associated with the tube to constitute an oscillatory circuit. The first cavity 10 has a hollow cylindrical inner conductor I2 and a'coaxially arranged hollow cylindrical outer conductor 13. A conductive rod 14 projects through inner conductor 12 and carries at one end a contact device I5 for yieldably engaging the grid radiator. This rod also supports a conductive cylinder 16 which is open at one end. The space between conductive cylinder 18, rod 14 and conductor 12 includes dielectric material TI and 18. With this construction, cylinder [6 in conjunction with conductor 12 and the intervening dielectric TI constitutes a blocking condenser for the grid. One end of outer conductor 13 is closed by a centrally apertured disc 80, apertured to acconmiodate the tube structure. Disc engages anode ring iii to couple the resonant cavity 10 therewith. The opcylindrical outer conductor 86. The ends of these conductors which are remote vfrom the triode tube are closed as indicated, and insulating spacers 81 maintain the conductors in'coaxial alignment. Other insulating-spacers 88, projecting from the closed end of outer conductor 86, facilitate mounting the generator arrangement to any supporting structure. A resilient contact device I03 for engaging anode ring SI of the tube is secured to outer conductor86.

A socket arrangement 90 is supported on a cathode post 9| conductively connected with the closed end of inner conductor and projecting through an aperture 92 in the closed end of outer conductor 86. The socket has inner and outer coaxially aligned contact members 93 and 94, re-

spectively, for receiving a heater prong and a cathode contact element 96. The circuits of contact members 93 and 94 extend through cathode post 9| to a terminal end to which a heater supply I00 may be coupled, as indicated.

electron discharge device,

7 Also, -a modulating-pulse input terminal III is coupled to cathode post I to permit the application of a modulating pulse of negative polarity to the cathode element.

. The described resonant cavities I0 and II are separable to permit inserting the tube into operative relation with reference thereto. A mechanical locking arrangement, designated I05, couples the resonant cavities into one assemblage after the tube has been inserted.

The arrangement of Fig. 3 also includes a spark-gap device IIO coupled into resonant cavity I0. To this end. one of the spark-gap electrodes III is connected with a magnetic-type coupling device II2 positioned within resonant cavity I0. The connection between these elements is afforded by a fuse clip II! engaging the terminal end of electrode III, and a mounting stud H4 projecting through outer conductor I3 of the cavity and supporting both fuse clip II I and coupling device H2. The modulating potential applied through terminal 02 to the grid structure of the oscillator is simultaneously applied'to the spark-gap device through a serially connected condenser connected in circuit between terminal 82 and the other spark-gap clectrode II5. This condenser is provided by a first conductive rod IIS and an associated conductive cylinder III closed at one end and spaced from rod I I6 by a. dielectric material III. The condenser element II! is conductively coupled to the terminal end of electrode H by means of a rod H9. The condenser elements are maintained in their desired spaced relation by an insulator I20, which may be molded thereabout. An'additional pair of concentrically aligned cylinders I2I and I22 are supported by the insula! tor I20. The first of these is conductively connected with rod II9 through a conductive member I23. The other is conductively connected with resonant cavity I0 by means of a strap I24 which also mechanically secures the spark-gap device and its associated condenser structures to the generator. Elements I2I and I2! constitute an air-dielectric condenser which completes an alternating current path from the spark-gap electrodes through coupling device H2 and the outer conductor I3 of resonant cavity I0.

Resonant cavity I0 has an electrical length} corresponding to substantially three-quarters of the operating wave length of the generator. The mounting strap I24 is secured thereto so that coupling device H2 is positioned in a portion of the cavity where the magnetic field has a maximum value. A further magnetic pickup device I is positioned in the same plane of resonant cavity I0 to derive the generated signal for application to a suitable utilizing circuit, as indicated by arrow I3I. This output. may be taken through a chimney-dike projection I32 of the outer conductor I3.

The generator of Fig. 3 is'similar to the wellknown Colpitts oscillator. It is operated with the anode electrode of the triode vacuum tube maintained at ground potential, as indicated by the connection I33. The first resonant cavity I0 is coupled between the anode and control electrodes of the tube. It may be considered as the wave-length determining portion of the oscillator. The other resonant cavity H is coupled between the anode and cathode electrodes. It is constructed to represent a capacitive reactance. The feedback required to sustain oscillations is provided by the interelectrode capacitance of the grid and cathode elements of the tube. The

conductors included in cathode post 0| for extending the circuits of socket 00 to the heater supply I00 may have such electrical lengths as to provide the usual radio-frequency chokes in the heater circuit. The excitation potential for initiating oscillations in the generator is applied with negative polarity to modulating-pulse terminals 82 and IM with such relative magnitudes that the grid is at a negative potential with reference to the cathode. The applied potential is also eflective to excite spark gap IIO through series condenser IIOII'I--II8.

The response of the generator to applied modlations have a high initial value and rapidly attain saturation value. In this manner a modulated-carrier signal envelope is produced having a leading sloped portion that occurs in approximate time coincidence with the corresponding portion of the modulating potential. Curves A, B and C of Fig. 2 also represent this operation of the Fig. 3 arrangement.

It will be apparent from the foregoing description and curves A and B of Fig. 2 that some time is required to provoke an arc discharge in the spark-gap device included in the generators of Figs. 1 and 3. This follows from the wave form of the modulating potential which, in most installations, has a finite leading slope and thus takes time to establish a potential across the spark gap equal to its breakdown potential. It is primarily for this reason that the generated signal represented by curve C lags the modulating potential by a very small interval. If desired, the spark-gap device may be controlled to cause the oscillatory circuit to have an increased background disturbance at the time of application of the modulating potential. An arrangement for accomplishing this result is represented in block diagram in Fig. 4. The signal generator is designated I50 and is influenced by thespark-gap device I5I. These units may be constructed as illustrated in Fig. 3. A modulating-potential source I52 which may comprise a multivibrator for supplying pulses of unidirectional potential of approximately rectangular wave form is directly coupled with the sparkgap device and is coupled to the generator through a time-delay network I53. With this circuit arrangement, the spark gap I5I is excited by a modulating potential leading that applied to the oscillatory circuit.

The operation of the Fig. 4 embodiment is indicated by the curves of Fig. 5. Curve E represents the leading modulating pulse applied to spark-gap device I5I to produce spark-gap current shown by curve F. The modulating potential of curve G applied to the generator I50 has a time delay Atz with respect to the potential of curve E. This time delay is such that the leading edge of the modulating pulse to generator I-50 occurs at an instant when the spark gap has increased the background disturbance of the generator. The resulting modulated-carthe present invention.

auasa.

especially its radiator, forms the subject matter oi an application Serial No. '649,346,-flled concurrently herewith in the name or Harold A. Wheeler, now Patent 2,439,641, issued April 18, 1948. Likewise an arrangement for coupling anode ring 81 to its associated resonators is disclosed and claimed in application Serial No. 649,-

345 filed concurrently herewith in the name of John A. Rado. Both the wheeler and Rado applications are assigned to the same assignee as The invention has been explained in the light of modulating potentials of approximately reotangular wave form., However, itls useful in connection with other dorms oi modulating potentials having sloped leading edges relied upon to initiate the operation of an oscillation generator.

While there have been described what are atv present considered to be the preferred embodiments of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

v 1; A modulated-signal generator comprising, an oscillatory circuit including a cavity resonator normally maintained in a nonoscillatory condition and having an inherent background disturbance the amplitude of which is normally much less than a predetermined value, means for applying to said oscillatory circuit a'pulse of modulating potential having a leading sloped portion to initiate therein oscillations of said predetermined value, a transient-signal generator positioned at least in part within said cavity resonator and having an operating interval not exceeding the duration of said leading sloped portion of said modulating potential, and circuit connections for exciting said transient-signal generator to introduce a signal into said cavity resonator effectively to increase the amplitude of said background disturbance to a level much greater than its normal value for an interval which occurs in approximate time coincidence with but of a duration not exceeding said'leading sloped portion of said modulating potential, whereby the oscillations initiatedin said circuit build up to said predetermined value rapidly to produce a modulated-carrier signal envelope with. a leading sloped portion occurring in approximate time coincidence with said sloped portion of said modulating potential. v

2. A modulated-signal generator comprising, an oscillatory circuit including a cavity resonator normally maintained in a nonoscillatory condition and having an inherent background disturbance the amplitude of which is normally much lessthan a predetermined value, means for applying to said oscillatory circuit a pulse of a in approximate time coincidence with said sloped modulating potential having a leading sloped portion to initiate therein oscillations of said predetermined value, a transient-signal generator including a spark-gap device positioned within said cavity resonator and having an operating interval not exceeding the duration of said leading sloped portion of said modulating potential, and circuit connections for exciting said traninitiated in said-circuit build up to said-prede- 4o mam tmm eflectively to increase the amplitude of said background disturbance t'o'a level much greater than its normal value for an interval which occurs in approximate time 00-* incidence with but of a duration not exceeding I said leading sloped portion of said modulating potential, whereby the 'oscillations initiated in said circuit build up to 1d predetermined value rapidly to produce a modulated-carrier signal envelope with a leading sloped portion occurring portion of said modulating potential.

1i, A modulated-signal generator comprising, an oscillatory circuit including a cavity resonator having an inner conductor and a concentrically arranged outer conductor, said oscillatory cir-' cuit beingnormally maintained in a nonoscillatory condition and having an inherent background disturbancethe amplitude of which is normally much less than a predetermined value, means for applying to one or said conductors of said oscillatory circuit a pulse of modulating potential having aleading sloped portion to initiate therein oscillations of said predetermined value, and a transient-signal generator having an operating interval not exceeding the duration of said leading sloped portion'oi said modulating potential, said transient-sisnalgenerator comprising a sparkgap devicepositioned within said cavity resonat/Jr with one electrode conductively connected to said one conductor and responsive to said modulating potential effectively to increase the amplitude oi said background disturbance to a level much greater than its normal value for an interval which occursin approxiy matetime coincidence with but of a duration not exceeding said leading sloped portion of saidv modulating potential, whereby the oscillations termined value rapidly to produce'a modulatedcarrier signal envelope'with a leading sloped portion occurring in approximate time coincidence with said sloped portion of said modulating potential.

4. A modulated-signal generator comprising, an oscillatory circuit including a cavity resonator having an innerconductor and a concentrically arranged outer conductor. said oscillatory circuit being normally maintained in a nonoscillatory condition and having an inherent background disturbance the amplitude of which is normally much less than a predetermined value,

' means for applying to one of said conductors of said oscillatory circuit a pulse of modulating potential having a leading sloped portion to initiate therein oscillations of said predetermined value, and a transient-signal generator having an operating interval not exceeding the duration of said leading sloped portion of said modulating potential, said transient-signal generator comprising a spark-gap device positioned within said cavity resonator with one electrode conductively connected to said one conductor, with a second electrode capacitively coupled to the other of said conductors and responsive to said modulating potential effectively to increase the amplitude of said background disturbance to a level much reater than its normal value for an interval which. occurs in approximate time coincidence with but of a duration not exceeding said leading sloped portion 'of'said modulating potential, whereby the oscillations initiated in said circuit build up to said predetermined value rapidly to produce a modulated-carrier signal envelope with a leading sloped portion occurring in approximate time coincidence with said sloped portion of said modulating potential. r

5. A modulated-signal generator comprising, an oscillatory circuit including a cavity resonator having an inner conductor and a concentrically arranged outer conductor, said oscillatory circuit being normally maintained in a nonoscillatory condition and having an inherent background disturbance the amplitude of which is normally much less than a predetermined value, means for applying to said inner conductor of said oscilla: tory circuit a pulse of modulating potential having a leading sloped portion to initiate therein oscillations of said predetermined value, and a transient-signal generator having an operating interval not exceeding the duration of said leading sloped portion of said modulating potential, said transient-signal generator comprising a spark-gap device positioned within said cavity resonator with one electrode conductively connected to said inner conductor, with a second electrode capacitively coupled to said outer conductor and responsive to said modulating potential effectively to increase the amplitude of said background disturbance to a level much greater than its normal value for an interval which occurs in approximate time coincidence with but of a duration not exceeding said leading sloped portion of said modulating potential, whereby the oscillations initiated in said circuit build up to said predetermined value rapidly to produce a modulated-carrier signal envelope with a leading sloped portion occurring in approximatetime coincidence with said sloped portion of said modulating potential.

6. A modulated-signal generator comprising, an oscillatory circuit including a cavity resonator normally maintained in a nonoscillatory condition and having an inherent background disturbance the amplitude of which is normally much less than a predetermined value, means for applying to said oscillatory circuit a pulse of modulating potential having a leading sloped portion to initiate therein oscillations of said predetermined value, a spark-gap device supported within said cavity resonator, and a condenser serially connected with said spark-gap device for applying said modulating potential thereto and comprising therewith a transient-signal generator having an operating interval not exceeding the duration of said leading sloped portion of said modulating potential for introducing a sig-' nal into said cavity resonator efiectively to increase the amplitude of said background disturbance to a level much greater than its normal value for an interval which occurs in approximate time coincidence with but of a duration not exceeding said leading sloped portion of said modulating potential, whereby the oscillations initiated in said circuit build up to said predetermined value rapidly to produce a modulated-carrier signal envelope with a leading sloped portion occurring in approximate time coincidence with said sloped portion of said modulating potential.

7. A modulated-signal generator comprising, an oscillatory circuit including a cavity resonator normally maintained in a nonoscillatory condition and having an inherent background disturbance the amplitude of which is normally much less than a predetermined value, means for applying to said oscillatory circuit a pulse of modulating potential having a leading sloped portion to initiate therein oscillations of said predetermined value, a spark-gap device at least partially positioned within said cavity resonator,

spark-gap device for simultaneously applying said modulating potential thereto and compris- 'ing therewith a transient-signal generator having an operating inter'valnotexceeding the duration of said leading sloped portion of said modulating potential for introducing a signal into said cavity resonator eflectively to increase the amplitude of said background disturbance to a level much greater than itsnormal value for an interval which occurs in approximate time coincidence with but of a duration not exceeding said leading sloped portion of said modulating potential, whereby the oscillations initiated in said circuit build up to said predetermined value rapidly to produce a modulated-carrier signal envelope with a leading sloped portion occurring in approximate time coincidence with said sloped portion of said modulating potential.

8. A modulated-signal generator comprising, an oscillatory circuit including a cavity resonator normally maintained in a nonoscillatory condition and having a inherent background disturbance the amplitude of which is normally much less than a predetermined value, means for applying to said oscillatory circuit a pulse of modulating potential having a leading sloped portion to initiate therein oscillations of said predetermined value, a spark-gap device having a pair of electrodes, a coupling device positioned within said cavity resonator and connected with one electrode of said spark-gap device, and av said leading sloped portion of said modulatin potential for introducing a signal into said cavity resonator effectively to increase the amplitude of said background disturbance to a level much greater than its normal value for an interval which occurs in approximate time coincidence with but of a duration not exceeding said leading sloped portion of said modulating potential, whereby the oscillations initiated in said circuit build up to said predetermined value rapidly to produce a modulated-carrier signal envelope with a, leading sloped portion occurring in approximate time coincidence-withv said sloped portion of said modulating potential,

9. A modulated-signal generator comprising, an oscillatory circuitnormally maintained in a nonoscillatory condition and having an inherent background disturbance the amplitude of which is normally much less than a predetermined value, means for applying to said oscillatory circuit a pulse of modulating potential having a leading sloped portion to initiate therein oscillations of said predetermined value, a transient-signal generator having a given starting time for efiective- 1y increasing the amplitude of said background disturbance to a level much greater than its normal value for an interval not exceeding the duration of said leading sloped portion of said modulating potential, and means for exciting said transient-signal generator earlier than said oscillatory circuit by an amount substantially equal to said starting time so that said background disturbance has its increased amplitude level at the time of application of said modulating potential to said oscillatory circuit, whereby the oscillations initiated in said circuit build up to said predetermined value rapidly to produce a modulated-carrier signal envelope with a leading sloped 13 portion occurring in substantial time coincidence with said sloped portion of said modulating potential.

10. A modulated-signal generator comprising,

an oscillatory circuit normally maintained in a' a level much greater than its normal value for an interval not exceeding the duration of said leading sloped portion of said modulating potential, and means for exciting said spark-gap device earlier thansaid oscillatory circuit by an amount substantially equal to said breakdown 14 time so that said background disturbance has its increased amplitude level at the time of application of said modulating potential to said oscillatory circuit, whereby the oscillations initiated in said circuit build up to said predetermined value rapidly to produce a modulated-carrier signal envelope with a leading sloped portion occurring in substantial time coincidence with said sloped portion of said modulating potential RUDOLF C. HERGENROTHER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date Mouromtsefl et al. Nov. 20, 1945 Varian Jan. 8, 1946 Hoiiman Apr. 1, 1947 Number 

